1. Field
The technology described herein relates to methods and apparatus for reduction of distortion in active devices.
2. Related Art
Most, if not all, active devices (e.g., amplifiers) exhibit non-linearity. FIG. 1A illustrates a conventional single stage amplifier 100. The amplifier 100 includes a transistor 110, illustrated as a bipolar junction transistor (BJT), in combination with an impedance 112. The transistor 110 receives an input signal Iin at its base terminal, and provides an output signal Iout at its collector terminal. The impedance 112 is connected between the emitter terminal of the transistor 110 and ground.
The non-linearity of the amplifier 100 is illustrated with reference to FIGS. 1B and 1C. As shown in FIG. 1B, the input signal Iin to transistor 110 is a two tone input signal, including a tone having a frequency f1 and a second tone having a frequency f2. The two tones have equal amplitudes Iin. The output signal Iout (shown in FIG. 1C) from the collector terminal of transistor 110 includes amplified signals at frequencies f1 and f2, having magnitudes I2. In addition, the output signal Iout is distorted, including tones at frequencies of 2f1-f2 and 2f2-f1, having magnitudes I3. These frequencies are known as intermodulation distortion. Other frequencies of distortion can be present, such as distortion at the harmonic frequencies of the input signals.